The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Spark ignition direct injection (SIDI) combustion systems (and other direct injection combustion systems) for internal combustion engines provide improved fuel economy and increased power over conventional port fuel-injected combustion systems. A SIDI engine includes a high pressure fuel injection system that sprays fuel directly into a combustion chamber. The fuel is directed to a specific region within the combustion chamber. As a result, a homogeneous or stratified charge may be created in the combustion chamber to provide improved fuel combustion characteristics. Also, throttling requirements associated with an SIDI engine tend to be less restrictive.
Referring now to FIG. 1, an exemplary SIDI engine 10 includes an engine block 12 that includes one or more cylinders 14. A spark plug 16 extends into a combustion chamber 18. The combustion chamber 18 is defined by a piston 20, the cylinder 14, and a cylinder head 21. The cylinder 14 includes one or more exhaust ports 22 and corresponding exhaust valves 24. The cylinder 14 includes also one or more intake ports 26 and corresponding intake valves 28. A fuel injector 30 extends into the combustion chamber 18. One or more of the fuel injectors 30 are connected to a fuel rail 32.
A fuel injection cycle of the SIDI engine 10 includes the delivery of fuel to the combustion chamber 18 via the fuel injectors 30 and the fuel rail 32. The fuel is injected in each cylinder once per combustion cycle. The injection typically occurs early in an intake stroke of the cylinder. The fuel is mixed with air in the cylinder and compressed during a compression stroke. At the end of the compression stroke the air/fuel mixture is ignited to provide a power stroke.
Although a SIDI engine tends to be more efficient during normal operation than a port-fuel injection (PFI) engine, a SIDI engine tends to generate more hydrocarbons during startup and cranking. Cranking refers to the initial rotating or crank over of an engine during startup. Since fuel is injected directly into a combustion chamber of a SIDI engine, there is less time for the fuel to mix with injected air than in a PFI engine. Thus, when the engine is cold, such as during cranking, less of the injected fuel burns and thus more hydrocarbons can be produced. The cooler the SIDI engine the larger the percentage of fuel that does not burn.